Arthropods are invertebrate animals with jointed limbs, a segmented body, and an exoskeleton. They belong to the phylum Arthropoda and include, but are not limited to arachnids, crustaceans, and insects.
Mosquitoes are considered the most dangerous animal in the world because of the number of disease organisms they can vector and the seriousness of these diseases to human and animal health (Schmidt 2005). Aedes aegypti is the principle vector of the viruses that cause dengue and yellow fevers (Gubler and Clark 1995, Robertson et al. 1996). Anopheles quadrimaculatus is the North American vector of the human malaria parasite (Foster and Walker 2009). Culex quinquefasciatus vectors St. Louis encephalitis and West Nile flaviviruses and filarial worms (Foster and Walker 2009). Personal repellents, applied to the skin or clothing can provide protection from mosquitoes and other biting arthropods. The gold standard insect repellent for the past 55 years is deet (N,N-diethyl-3-methylbenzamide). Deet provides good repellency against many mosquito species (Fradin and Day 2002, Frances 2007a) but has been criticized for its odor and skin feel and the fact that it is a plasticizer. Additionally, some incidences of toxicity have been reported (Clem et al. 1993, Veltri et al. 1994, Goodyear and Behrens 1998). Although the number of confirmed negative reports of deet toxicity is extremely small compared to the number of people who use deet, a portion of the population chooses to avoid products containing deet, thereby putting them at risk for mosquito-vectored disease.
Ticks are ectoparasitic obligate blood-feeders and important vectors of human and animal pathogens (Sonenshine 1993). Ticks pose serious concerns for humans, both in the number and range of disease organisms that they can vector and in localized allergic reactions at the bite site. Two tick species, the American dog tick, Dermacentor variabilis the lone star tick, Amblyomma americanum, are commonly found attached to people in the southern and eastern U.S. (Merten and Durden 2000). Dermacentor variabilis is the primary vector of Rickettsia rickettsii, the causative agent of Rocky Mountain Spotted Fever, in the eastern U.S. Amblyomma americanum is an aggressive tick that is a carrier of a number of organisms that can cause disease in humans including Ehrlichia chaffeensis, E. ewingii, and Rickettsia amblyommi (Schulze et al. 2011) and has been implicated as the vector of the novel phlebovirus, Heartland virus (McMullan et al. 2012). Amblyomma americanum also vectors Southern Tick Associated Rash Illness (STARI), which causes symptoms similar to Lyme disease, but whose etiological agent has yet to be conclusively identified (Masters et al. 2008). A third important tick species in the U.S. is the black-legged tick, Ixodes scapularis. This tick is the vector of the Lyme disease spirochete, Borrelia burgdorferi in eastern North America and the protozoans that cause human babesiosis (Nicholson et al. 2009). A fourth tick of importance is the brown dog tick, Rhipicephalus sanguineus. This tick exhibits a cosmopolitan distribution and is primarily a canine ectoparasite but also bites humans, can vector R. rickettsii, and can infest households in large numbers (Nicholson et al. 2009).
Bed bugs are parasitic insects of the cimicid family that feed on the blood of a host. Cimex lectularius, is the most common bed bug; it prefers to feed on human blood. Other Cimex species are specialized to other animals, e.g., bat bugs, C. pipistrelli (Europe), C. pilosellus (western US), and C. adjunctus (entire eastern US). A number of adverse health effects may result from bed bug bites, including skin rashes, blisters, psychological effects, and allergic symptoms. Adult bed bugs are light brown to reddish-brown, flattened, oval-shaped and have no hind wings. Like other parasites, bed bugs are attracted to their hosts by host cues—primarily carbon dioxide, secondarily by warmth, and also by certain chemicals. Bed bug infestations have been on the rise in the past decade. Resistance to traditional chemical pesticide treatments has also increased, making eradication even more difficult.
Fleas are insects from the order Siphonaptera. They are wingless, external parasites, that feed on the blood of a host. Fleas attack a wide variety of warm-blooded vertebrates including dogs, cats, humans, chickens, rabbits, squirrels, rats, ferrets, and mice. Flea bites can result in skin irritation and allergic reactions. Fleas are vectors for many viral, bacterial, and rickettsial diseases in humans and other animals. Notably, fleas were in part responsible for the bubonic plague epidemic by transmitting bacteria between rodents and humans. Resistance to traditional chemical pesticide treatments has also increased, making eradication even more difficult.
Flies are insects of the order Diptera. They have a pair of wings on the mesothorax. Flies are not only a nuisance but also are vectors of disease transmission. Some diseases transmitted by flies include typhoid, cholera and dysentery salmonella, anthrax, and tuberculosis.
Personal repellents are a key protection measure against arthropods such as mosquitoes ticks and provide a line of defense against the diseases that they may transmit. In addition to efficacy, a number of factors influence the use rate of personal repellents including safety (whether actual or perceived) and aesthetics such as skin feel and odor. There are many commercially available mosquito repellents; however, only four active ingredients are recommended for use in the U.S. by the CDC: deet, IR3535, Picaridin, and PMD. Deet has been shown in many studies to exhibit good repellency against numerous mosquito species. Although deet has been used for decades with relatively few reports of toxicity, the belief that deet is a health and environmental hazard still exists for some people (Aquino et al. 2004). IR3535 and Picaridin are two alternatives to deet that exhibit good aesthetic characteristics and low mammalian toxicity (Nentwig 2003, Frances 2007b, Moore and Debboun 2007); however, both are registered pesticides with the Environmental Protection Agency (EPA). PMD exhibits low rat oral and rabbit dermal toxicity, but is exceptionally irritating to the eyes and can cause irreversible eye damage (Strickman 2007). Current recommendations by the U.S. Centers for Disease Control and Prevention (2012) for prevention of tick bites are the use of a repellent containing ≥20% deet (N, N-diethyl-m-toluamide) on skin or the toxicant permethrin on clothing.
Formulation can play a critical role in extending repellent efficacy. For example, a liposomal formulation of deet provided complete protection on treated rabbits against attachment of adult D. variabilis and A. americanum ticks for 72 h compared to no protection by a standard formulation of deet (Salafsky et al. 2000). In another study, a polymer formulation of deet and cream formulations of Picaridin and SS220 provided almost complete repellency to nymphal A. americanum for 12 h (Carroll et al. 2008). The plant-derived repellent, unformulated 2-undecanone provided 74% repellency against D. variabilis 2 h after application (Kimps et al. 2011) compared to 98% repellency from 3-3.5 h after application when formulated in the product BioUD® (Bissinger et al. 2009). Most published research has focused on repellent active ingredient identification rather than formulation and formulation chemistry is often a guarded secret of private industries (Bissinger and Roe 2010).
A number of plant-based repellents are available commercially; in many cases because of their rapid registration process under the US EPA's FIFRA section 25(b), which provides exemption from federal registration for specific ingredients that are deemed demonstrably safe for their intended use. Many of the ingredients on the 25(b) list are highly volatile compounds, causing them to provide only short-term repellent duration. Increasing the concentration of active ingredient can lengthen the duration of repellency; however, many essential oils are irritating to the skin above a certain concentration (Barnard 1999). Additionally, the aesthetics (e.g., odor, appearance, tactile, residual odor, discoloration, etc.) of many plant-based repellents are poor. Moreover, most repellents are developed for use against mosquitoes rather than arthropods in general (e.g. ticks), making efficacy data on arthropod repellency less available (Bissinger and Roe 2010). Therefore, there is a need for a broad-spectrum arthropod repellent that provides a high level of repellency for an extended amount of time while simultaneously exhibiting desirable aesthetics, such as pleasant odor and skin feel.
One advantage of the present compositions used in the methods of the present invention is that compositions can be produced containing only ingredients exempt from EPA registration by virtue of their appearance on the FIFRA 25(b) list or Class 4(a) inert ingredient list making the composition completely safe for use, and potentially eligible for classification as an organic pest control agent.